It is well known that in the electronics industry, particularly the personal computer industry, the trend is to design products which are smaller, lighter, and more compact while maintaining or increasing power, speed, and memory capacity. In recent years, the computer industry has experienced the advent of the lap-top computer, the notebook computer, and now the palm-top computer. Although these computers are amazingly compact and lightweight, they are still incredibly powerful and fast. They are capable of running software applications that only in the recent past were able to be run on desk-top computers with large amounts of memory.
Personal computers (including desk-top, lap-top, notebook, and palm-top computers) include a mother board for controlling the operation of the computer. Personal computers are sold with a specified amount of memory, for example 10 gigabytes (GB) of storage memory on a hard drive and 64 megabytes (MB) of random access memory (RAM). Mother boards typically include standardized slots in which boards for memory, sound, video, and graphics may be inserted.
In the case of memory boards or memory modules, a dual in-line memory module (DIMM) connector is a standard industry connector for receiving a module. In accordance with the "smaller-is-better" trend in the computer industry, many mother boards are equipped with only two DIMM connectors. As such, in order to install a large amount of memory in only two DIMM connectors, higher density memory modules have been developed. As used herein, the term "memory module" is not strictly limited to memory boards, but also includes similarly configured circuit boards designed for computers and computer related products which include integrated circuit chips.
One conventional technique for increasing the storage capacity of a memory module is to increase the height of the module. For example, the storage capacity of a memory module having two rows of memory chips can be increased by a factor of two by adding a third and fourth row of memory chips. However, there are two primary disadvantages of such a configuration. One disadvantage is the increase in height of the module. The housing of the computer and the area around the mother board both need to be sufficiently large in order to accommodate the increase in height of the module, which runs contrary to the small is better design principle. Another disadvantage lies in different trace lengths. A trace is the electrical conductor which connects the chips to the edge connector or interface portion of the module. In a triple row configuration, the first, second and third row of chips each have their own trace lengths such that the first row of chips being closest from the edge connector, the third row of chips being furthest from the edge connector, and the second row of chips being between the first and third row of chips. The trace of the third row of chips is essentially three times as long as the first row of chips. In a similar fashion, the trace of the second row of chips is essentially twice as long as the first row of chips. Accordingly, a signal traveling to the furthest row of chips takes about three times as long to arrive as the signal traveling to the first row of chips. This arrangement requires the signal delay to be eliminated, which may be done by synchronizing the signals, which is difficult and expensive to accomplish. Alternatively, the trace of the closer row of chips may be physically lengthened so that the signals arrive at the three rows at about the same time. Either solution results in a module which is limited in speed by the double and triple-length traces.
Another conventional technique for increasing the storage capacity of a memory module is to configure the double-height arrangement discussed above with a foldable portion such as an integral flex conductor. The module may then be folded in half, thereby reducing the height essentially by two. However, this foldable configuration still suffers from the drawback of the varying trace lengths. An additional drawback is created by the folded arrangement in that vertical air circulation is restricted. The components of the module produce heat, and under normal convection the heated air would rise and be drawn out of the computer by a fan. However, the folded portion of the module retains heat between the folded sections, which may cause the module to function improperly and errant.
In addition to memory modules and other types of boards, lap-top, notebook, and palm-top computers generally interface with PC cards such as RAM cards, ATA flash cards, modem cards, and various other types of cards. There is a particularly strong driving force to densely package the integrated circuit chips due to the relatively small size of the PC cards which are usually the size of a typical credit card. For the same reasons discussed above in regards to the memory modules for mother boards, it is preferable to increase chip capacity without increasing the dimensions of the PC card. For example, adding additional rows of memory chips would require a larger circuit board which would necessitate increasing the size of the PC card and varying the trace lengths. Using integral flex conductors may necessitate increasing the thickness of the PC card to an unacceptable level. The foldable configuration also suffers from the drawback of the varying trace lengths.
Accordingly, in view of the foregoing, it is an object of the present invention to provide an integrated circuit package which overcomes the disadvantages and drawbacks associated with conventional modules and circuit boards.